1. Field of the Invention
The present invention relates to a clutch disk assembly and in particular to a clutch disk assembly whose torsion characteristics have a low spring constant area at a first stage for preventing a rattling noise.
2. Description of the Related Art
In general, a clutch disk assembly whose torsion characteristics have a low spring constant area at a first stage for preventing a rattling noise is frequently used in a manual transmission type vehicle. Since it is well known that the low spring constant area is also deemed as a cause of the transient surge or backing which occurs upon acceleration operation during the vehicle's travel, how to concurrently cope with both the rattling noise and the trangient surge is one important problem to be solved.
One of the improvements for solving this problem is disclosed in Japanese Patent Publication No. 40125 of 2nd year of Heisei (1989). That clutch disk assembly is shown in FIG. 9 and includes an inner hub 1 and an outer hub 2. Between the hubs 1 and 2, there is interposed a first spring 3 of a low spring constant which constitutes a first stage of the torsion characteristics of the clutch disk. In addition, between the outer hub 2 and a side plate (not shown), a second spring 4 is interposed which constitutes a second stage of the torsion characteristics of the clutch disk.
While a small amount of torque is applied to the clutch disk, the relative rotation between the inner hub 1 and the outer hub 2 is established within an angle in the circumferential direction of the clutch disk, and the first torsion spring is operated or actuated, which constitutes the low spring constant area as a first stage of the torsion characteristics. Thus, the rattling noise upon idle rotation of the clutch disk is prevented.
When the relative rotation between the inner hub 1 and the outer hub 2 proceeds and the foregoing circumferential angle exceeds a certain value as a result of the increased torque, the inner hub 1 and the outer hub 2 are brought into a unitary movement which results in the cessation of operation of the first torsion spring 3. Simultaneously, due to the relative movement between the outer hub 2 and the side plate, the second torsion spring 4 begins to operate, resulting in that the constitution of the spring constant area of the torsion characteristics in order to absorb the inputted torque variation.
At this time, when the second torsion spring 4 is brought into deflexion as a result of the relative rotation between the outer hub 2 and the side plate, a distal end of a receiving extension of the second torsion spring 4 begins to urge or bias a cam 6 for the rotation thereof in the counter-clockwise direction which is disposed between the inner hub 1 and the outer hub 2. That results in the establishment of the locked condition of the inner hub 1 relative to the outer hub 2 due to the mesh engagement between a geared portion 1a and a geared portion 2a.
Under the resulting condition, upon reverse of the torque, the second torsion spring 4 is extended, thereby returning the receiving extension 5 thereof to its original or initial position.
At this time, if the reverse of the torque is performed at a slow speed, the cam 6 is brought into the clockwise rotation due to the urging of the receiving extension 5 of the second torsion spring 4, thereby releasing the locked condition of the inner hub 1 which enables the operation of the first torsion spring 3. Contrary to this, if the reverse of the torque is performed at a high speed under which transient surge or backing may occur, a frictional force at a position p in FIG. 11 between the cam 6 and the geared portion 1a with which the cam 6 is engaged continues to maintain the locked condition between the inner hub 1 and the outer hub 2. Thus, the transient surge or backing can be prevented upon acceleration operation during vehicle's travel.
However, in the foregoing clutch disk assembly, in the case of soft on and off operation of an accelerator, due to the slight deflection of the second torsion spring 4, the rotation of the cam 6 by the movement of the receiving extension 5 of the second torsion spring 4 is not established. Thus, the vehicle continues to travel under the unlocked condition between the inner hub 1 and the outer hub 2, under which the prevention of transient surge or backing can't be attained.
In addition, when a torque in the negative direction is applied to the cam 6 which is in the locked condition, the entire torque is set to be received by a supporting shaft 6a of the cam 6. In light of the fact that the cam 6 is interposed between the inner hub 1 and the outer hub 2, the cam 6 is set to be located at a position of an inner side of the clutch disk. This leads to an excess increase of the load applied to the supporting shaft 6a of the cam 6. Thus, an increase in the rigidity or stiffness of the supporting shaft 6a of the cam 6 is required, and the second torsion spring 4 must be located outside the clutch disk. The resulting arrangement or structure inevitably leads to clutch disk assembly of scaled up size.